Multiline means that a slot machine has several lines that you can play and win on. All modern slot machines are multiline so nowadays the term is not used very often. Instead, online casinos usually specify how many lines a gaming machine has, for example, 10 or 25. The older slot machines with only three wheels usually only have one line to play on. As the modern videoslots with 5 reels were introduced at online casinos, they were called multiline slots.